Fuel injection system for internal combustion engines

ABSTRACT

A fuel injection system having a reciprocating control member driven in synchronism with the injection pump for opening a fuel bypass and interrupting the injection process. The control member, during its return stroke, drives the fluid through a controllable throttle channel to create a &#39;&#39;&#39;&#39;fluid abutment,&#39;&#39;&#39;&#39; i.e., it does not return to the initial position. A second bypass is provided subject to control by the control member as well as by a slide valve; also synchronous with the main pump, the characteristic feature being the coordination of the control member with the slide valve in dependence on the variable position of the fluid abutment and a throttling restriction provided in the second bypass.

United States Patent [72] inventors GenldHoier;

Heinz Nothdurlt, both of Stuttgart, Germany [211 App]. No. 63,215

[22] Filed Aug. 12, 1970 [45] Patented Nov. 16, 1971 [73] Asaignee Robert Bosch GmbH t- Gummy [32] Priority Sept. 19, 1969 [33] Germany [54] FUEL INJECTION SYSTEM FOR INTERNAL AM, 139 BB, 140 A, 140 F6; 417/300, 293, 302, 303, 304

[56] References Cited UNITED STATES PATENTS 3,403,629 10/1968 Eheim et a1 417/293 3,320,893 5/1967 Koster et a1 417/293 FOREIGN PATENTS 968,513 9/1964 GreatBritain.............0.. 123/139 AM Primary Examiner- Laurence M. Goodridge Assistant Examiner-Cort Flint Anomey-Edwin 1E. Greigg ABSTRACT: A fuel injection system having a reciprocating control member driven in synchronism with the injection pump for opening a fuel bypass and interrupting the injection process. The control member, during its return stroke, drives the fluid through a controllable throttle channel to create a fluid abutment, i.e., it does not return to the initial position. A second bypass is provided subject to control by the control member as well as by a slide valve; also synchronous with the main pump, the characteristic feature being the coordination of the control member with the slide valve in dependence on the variable position of the fluid abutment and a throttling restriction provided in the second bypass.

PATENTEU 15 3.620.648

SHEET 1 OF 2 Fig. I

PATENTEDunv 1s l97| 3, 620,648

sum 2 OF 2 FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES FIELD OF THE INVENTION The invention relates to a fuel injection system for internal combustion engines.

BACKGROUND OF THE INVENTION A system of this type is known in which the amount or rate of fuel is variable in dependence on the rpm. by interruption of the delivery at least upon attainment of the maximum r.p.m. owing to the opening of a first bypass of the injection pump work chamber during the pressure stroke of the pump piston by means of a reciprocating control member, which is driven during its pressure stroke by the pressure liquid supplied from an auxiliary pump operating in synchronism with the injection pump, and which is decelerated during the return stroke thereof by means of a throttle channel having a restriction through which at least a portion of the liquid supplied during the pressure stroke is made to flow during the return stroke, whereby the control member upon the attaining of a predetermined r.p.m. and at a certain value of the cross-sectional area of the restriction owing to the occurrence of a fluid abutment" does not return to the initial position on a fixed stop provided therefor, a second bypass conduit being provided for the work chamber and which is controlled by the control member and by a slide valve operating in synchronism with the injection pump and with the auxiliary pump.

A system of this type is known from German Pat. No. 1,286,804. In the known system, the second bypass is blocked by the control member during the starting of the engine, and, furthermore, as long as the control member returns to its initial position (no fluid abutment) or the fluid abutment is below a predetermined level, it is opened by the injection pump piston before the control member opens the first bypass. With such a control of the second bypass channel, means are provided for preventing within the full load range of r.p.m.

.that the pressure liquid of the auxiliary pump flowing away through a release channel for supplying supplementary fuel during the starting process will detrimentally affect the control process.

In diesel engines there appears a marked combustion noise, particularly in the low load range of rpm. and in the idling state. This is caused, apart from thermal conditions, by the relatively low duration of the injection process corresponding to the small amount of fuel to be injected under these conditions. It is possible to substantially reduce this combustion noise by extending the duration of the injection process, for instance, by extending the effective period of supply for each pressure stroke of the injection pump.

Such an extension of the injection is obtained by means of the so-called preinjection processes, in which first a small amount and then the main amount of fuel is injected. In a known fuel injection system of this type according to French Pat. No. 1,495,537, as well as the first Addition No. 92,335 thereto, the bypass is connected to a hydraulic storage means, the pressure characteristic of which is variable in order to modify the injection process. However, this arrangement is costly and complicated and, in the region of high partial or full loading it has a detrimental effect on the injection, since even if the piston of the storage means is blocked within this range of rpm, the construction entails an enlargement of the dead space of the work chamber.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to provide a fuel injection system of the type described above, in which simple means are provided for extending the duration of the injection process in the idling state and at least within the low range of partial loading but not in that of full loading.

This is achieved by a dimensioning of the system whereby the second bypass is opened by the control member before the first bypass and, in the absence of fluid abutment, is closed by the slide valve before being opened by the control member, whereas in the presence of the fluid abutment, it is opened by the control member for increasing levels of the fluid abutment at an increasingly earlier time relative to the earlier closing thereof by the slide valve, a throttling restriction being provided in the second bypass.

The duration of the supply interval is extended by means of a calibrated throttle passage connecting the injection pump work chamber in the idling state and in the state of partial loading with a low-pressure space, whereby the amount of fuel supplied by the injection pump is divided into two partial flows, only one of which is injected. The switching off of the second partial flow under partial load conditions then takes place with a smooth transition.

In accordance with a favorable embodiment of the invention, the throttle area is controllable.

The slide valve may be the piston of the main injection pump or that of the auxiliary pump, as is known per se.

In an embodiment, in which the bypass control member is provided with a peripheral notch and a longitudinal notch connecting therewith, an end surface may be provided for delimiting the longitudinal notch in the axial direction and controlling the second bypass throttling restriction being provided in the longitudinal notch.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention is shown in diagrammatic form in the drawing and will be described in more detail below.

FIG. 1 is a longitudinal section through the fuel injection system.

FIG. 2 is a modified form of the control member with the throttle area thereof shown in partial longitudinal section.

FIG. 3 shows the control member of FIG. 2 in cross section taken on line Ill-III of FIG. 2.

FIG. 4 shows diagrams illustrating the rate of fuel supply, the stroke of the control member and that of the injection pump piston as functions of the angular position of a cam driving the system.

DESCRIPTION OF THE EMBODIMENTS With reference to FIG. 1, there is shown a housing 1 of a fuel injection pump having a combined slide valve and piston 2 operating in a cylinder 3 and delimiting therewith a work chamber 4. Piston 2 is reciprocated by means not shown, as illustrated by the arrows in FIG. 1, and simultaneously therewith rotates about its axis. During each suction stroke of piston 2, fuel is supplied to work chamber 4 from a suction chamber 5 via suction borings 6 and one of a plurality of Iongitudinal notches 7 on the piston, an annular notch 8, and an axial bore 9, which connects with notch 8 through a transversal bore 10 and which ends in work chamber 4.

Via a distributing longitudinal notch 11, piston 2 delivers fuel sequentially to supply conduits 12, in each of which there is provided a nonretum valve 13 with a release piston 13, and which are connected to fuel pressure lines, not shown, leading to the different injection valves of the engine. Nonreturn and release valve 13, in a manner known per se, prevents a delayed spurious injection from taking place after the termination of the actual injection process owing to pressure variation and elasticity in the fuel pressure line as well as the compressibility of the fuel. Longitudinal notches 7, only two of which are shown, and supply conduits 12, of which only one is shown, are spaced uniformly around the circumference of piston 2 and of cylinder 3 in a number corresponding to the number of cylinders of the engine to be supplied with fuel from the pump. Whereas suction bore 6 and supply conduit 12 are in the same plane, distributing notch 11 and notches 7 are staggered, since notch 11 opens up one of the supply conduits when the longitudinal notches 7 are disconnected from suction bore 6 and vice versa.

The injection rate is controlled by a control member 14-in the form of a slide valve. Control member 14 operates in a cylinder 15 and controls the connection between one section 160 of a bypass channel leading from work chamber 4 to cylinder 15 and the other section 16b leading from cylinder 15 to suction chamber 5. Control member 14 has an annular notch 17, which is in continuous connection with channel section 16a and is disconnected from section 16b in the inoperative position shown in FIG. 1.

A section of the main pump piston system is of larger diameter and forms the piston 18 of an auxiliary pump operating in a cylinder 19. The liquid displaced by piston 18 actuates control 'member 14 during its pressure stroke. Connecting with the end surface area of piston 18 are longitudinal notches 20 provided on the cylindrical surface thereof in a number corresponding to that of notches 7 and in the same planes as the latter. Suction borings 21 are provided to cooperate with notches 20 and during the suction stroke of piston 18 fuel flows from suction chamber 5 into the work chamber of auxiliary pump 18, 19. Piston 18 during the subsequent pressure stroke displaces fuel substantially via notches 20 and a channel 22 into cylinder 15 in front of control member 14. Channel 22 and suction borings 21 are staggered relative to each other.

As control member 14 is displaced from its inoperative position by auxiliary pump 18, 19, it establishes a connection between channel sections 16a and 16b shortly before the end of its operative stroke. The inoperative position is determined by fixed stop 23 provided in cylinder 15 under the piston. During the return stroke, control member 14 is driven by a return spring 24 and displaces at least a portion of the liquid which caused the operating stroke thereof back via a channel 25 into cylinder 19 of the auxiliary pump, channel 22 being then closed by a nonretum valve 26. Channel 25 has interposed therein a cylinder 27, in which a slide valve 28 is axially adjustable by means of a screw 29. Provided on slide valve 28 is an annular notch 30, with which the section of channel 25 leading from cylinder 15 connects freely, whereas the section of channel 25 connecting with cylinder 19 can be throttled by slide valve 28 at the point 31 where it ends in cylinder 27.

The return stroke of control member 14 is decelerated to a greater or lesser extent depending upon the cross-sectional area of the throttle aperture 31. Above a value of r.p.m. determined by aperture 31, the pressure stroke of auxiliary pump 18, 19 sets in before control member 14 could return to its initial position. This represents a fluid abutment" for control member 14, owing to which it will start its forward stroke from another initial position, whereby channel sections 16a and 16b are interconnected at an earlier time. This leads to a decrease in the amount of fuel supplied and therefore also in the r.p.m. of the engine supplied from the injection system. The forward stroke of control member 14 in any case terminates when the lower edge thereof opens up a safety bore 32 connecting with suction chamber 5 and through which the remainder of the fuel supplied from auxiliary pump 18, 19 is drained off.

Before control member 14 opens up bypass channel 16b, it opens a second bypass channel 33, which also connects with suction chamber 5. Channel 33, however, is interrupted by cylinder 3, in which piston 2 operates. For the control of channel 33 there is provided on the cylindrical surface of piston 2 an annular notch 34, through which the second bypass is held open as long as piston 2 is in its lower inoperative position, whereas it is closed after the pump piston has performed a certain fraction of its pressure stroke. This fraction of the stroke which is required to be performed by piston 2 in order to close bypass channel 33 is selected in such a manner that at full load, i.e. as long as control member 14 returns to stop 23, channel 33 is closed by piston 2 before the control member 14 opens channel 33. However, as soon as a fluid abutment is present, channel 33 is opened by the control member 14 before piston 2 has performed the said fraction of its stroke. Therefore, a portion of the fuel delivered by piston 2 will flow via channel section 16a, annular notch 17 and second bypass 33 into suction chamber 5 until the second bypass is blocked by piston 2.

Provided in second bypass channel 33 is a throttling restriction 35 which can be adjusted at will with the aid of an adjustment screw 36.

FIGS. 2 and 3 illustrate a modified forrn 14a of the control member, in which a restriction 35a is provided between member and cylinder 15. Provided on control member 14a in connection with annular notch 17 are longitudinal notches 37 and 38 for controlling channels 161: and 33. Notch 37 controls channel 33 and is provided close to its end at notch 17 with a throttling restriction 35a.

The operation of the system will be described with reference to the diagrams of FIG. 4 illustrating the extension of the injection process caused by restriction 35 or 35a in the idling or low load range.

The top diagram shows the amount of q of fuel supplied, the middle diagram the portion S, of its stroke performed by control member 14, and the bottom diagram the portions S, of its stroke performed by piston system 2, 18 as functions of the angle of rotation a of a driving means, such as a cam, causing the reciprocation of piston system 2, 18.

The top diagram shows three graphs (Vl, Vii, VIII) of the amount of fuel supplied, the middle diagram shows four characteristics (1, 11, ill, IV) for the path 8, of the control member and the bottom diagram is a graph V illustrating the sinusoidal movement of piston 2, 18, i.e. the path S thereof.

The horizontal line S of the middle diagram shows the portion of the stroke that has to be performed by control member 14 from fixed stop 23 before second bypass channel 33 is opened (intersection of line S with characteristics 1 to ill). Horizontal line S shows the portion of the stroke of the control member from fixed stop 23 which is required for section 161: of the first bypass to be opened (intersections of line 5,, with characteristics 1 to 1V). Characteristic 1 (shown in full lines) shows the movement performed by control member 14 as long as it is able to return to stop 23. Characteristics II to IV (in dash lines, dot-dash and full lines, respective) show the movement of control member 14 for difierent increasing levels of the fluid abutment designated 5,, S, and 5,, respectively. The horizontal line 8,, of the lower diagram shows the position of piston system 2, 18 in which suction borings 6 and 21 are closed by pistons 2 and 18, respectively, and the forward stroke of control member 14 begins. This occurs at the angular position a At angular position a when piston system 2, 18 has performed the portion 8,, of its stroke, annular notch 34 is disconnected from the second bypass channel 33, which is then blocked.

As soon as piston system 2, 18 has moved through distance S suction borings 21 are opened through the action of iongitudinal notches 20 making it possible for the fuel displaced by piston 18 to flow back into suction chamber 5. From this moment on, as is apparent from the middle diagram, the return stroke of control member 14 begins under the influence of return spring 24 and causes fuel to be displaced via restriction 31 and to brake the movement of the control member to a greater or lesser extend depending on the cross-sectional area of the restriction. The distance S corresponds to angular position 01 Since characteristic 1 (middle diagram) is on the intersection of lines 3 and a it is apparent that as long as the control member 14 returns to its fixed stop 23, i.e. as long as no fluid abutment is operative, second bypass 33 is already disconnected from annular notch 34 when it is opened by control piston 14.

1n the top diagram, characteristic Vl illustrates the amount of fuel supplied by injection pump piston 2 in the entire range of full load r.p.m.a. However, as soon as a fluid abutment is present, for instance at the level 5: corresponding to position a: (middle diagram), as represented by dash-line characteristic II, the second bypass is opened up by control member 14 at angular position a, (intersection a S whereby, if restriction 35 is fully open, the fuel displaced by piston 2 is diverted into suction chamber 5. Not until the second bypass is blocked by piston 2 at angular position a does the fuel flow into conduit 12, until, at angular position m, the injection is interrupted by the control member in the position S opening section 161: of the first bypass (intersection S -m). The amount of fuel delivered in that condition is shown by graph VII of the top diagram.

As soon as the fluid abutment has risen to the level S (middle diagram), as shown by dash-dot characteristic III, the partial flow through second bypass 33 sets in already at angular position a and at position a section 16b of the first bypass is opened up, whereby the injection process is terminated (intersection of characteristic III with S,.,). The amount of fuel supplied in this condition is shown by curve VIII of the top diagram.

If the fluid abutment rises further, no injection takes place. From a certain level upwards, such as level S of the middle diagram, control member 14 in its position S opens up safety bore 32, whereby its maximum stroke is determined. After the opening of safety bore 32, characteristic IV is horizontal and, like the other characteristics, drops off again beginning at position a It is apparent that the amount of fuel injected decreases as the fluid abutment rises, i.e. with a decrease in loading. In this condition corresponding to partial loading or to idling in accordance with graphs VII and VIII, there is first injected a smaller quantity in an amount depending on the loading condition, after which a break sets in, and at the termination thereof when the second bypass has been shut ofi by the piston 2, the main fuel quantity is injected.

When the throttling restriction 35 is adjusted to a smaller cross-sectional area, the inclinations of graphs VII and VIII between positions a: or 11 respectively, any position a (horizontal sections shown in upper diagram) vary according to the r.p.m. owing to the increase in throttling effect with the increasing r.p.m., i.e. decreasing duration of the flow, so that from a certain high value of r.p.m. on, the throttling effect of restriction 35 is large enough to cause the inclination of graphs VII and VIII within this range to be approximately as large as that of curve VI. If the restriction 35 were closed completely, graphs VII or VIII would coincide with graph VI; however, they would end at the intersection with the ordinate a, or 0 respectively.

That which is claimed is:

l. A fuel injection system for internal combustion engines having a variable rate of fuel supply in dependence on the r.p.m., comprising,

a fuel injection pump having a cylinder and a pump piston in said cylinder delimiting therewith a work chamber,

a first bypass for said work chamber, a reciprocable control member for interrupting the delivery of said pump at least at maximum r.p.m. by opening up said first bypass during the pressure stroke of the said pump piston,

an auxiliary pump for operation in synchronism with said injection pump and supplying pressure liquid to said control member during the pressure stroke thereof means for exerting a return force on said control member,

a stop for limiting the return stroke of said control member and defining a fixed initial position therefor,

a throttle channel having a controllable restriction therein and connected to receive a portion of the liquid displaced during the return stroke of said control member, thereby to decelerate said return stroke,

whereby said control member upon the attaining of a predetermined r.p.m. and at a certain value of the crosssectional area of said restriction is subjected to a fluid abutment and does not return to said initial position,

a second bypass connected with said work chamber and means on said control member for controlling said second bypass,

a slide valve driven in synchronism with said injection pump and said auxiliary pump for controlling said second bypass,

characterized by a dimensioning of said system, whereby said second bypass (33) is opened up by said control member (14) before said first b ass (16), said second bypass (33) in the absence of a fluid abutment being closed by said slide valve (2) before being opened by said control member (14) and in the presence of said fluid abutment being opened by said control member (14) for increasing levels of said fluid abutment at an increasingly earlier time relative to the earlier closing thereof by said slide valve (2), a throttling restriction (35) being provided in said second bypass 33).

2. A fuel injection system according to claim I, in which the cross-sectional area of said throttling restriction (35) is variable.

3. A fuel injection system according to claim 1, in which said slide valve (2) comprises the piston of said injection pump.

4. A fuel injection system according to claim 1, in which said slide valve (2) comprises the piston (18) of said auxiliary pump.

5. A fuel injection system according to claim 1, in which there are provided on said control member (14) for controlling said bypasses (16, 33) an annular notch (17), a longitudinal notch (37) connecting therewith and an end surface delimiting said longitudinal notch (37) in the axial direction for controlling said second bypass (33), said longitudinal notch (37) having a throttling restriction 35a. 

1. A fuel injection system for internal combustion engines having a variable rate of fuel supply in dependence on the r.p.m., comprising, a fuel injection pump having a cylinder and a pump piston in said cylinder delimiting therewith a work chamber, a first bypass for said work chamber, a reciprocable control member for interrupting the delivery of said pump at least at maximum r.p.m. by opening up said first bypass during the pressure stroke of the said pump piston, an auxiliary pump for operation in synchronism with said injection pump and supplying pressure liquid to said control member during the pressure stroke thereof, means for exerting a return force on said control member, a stop for limiting the return stroke of said control member and defining a fixed initial position therefor, a throttle channel having a controllable restriction therein and connected to receive a portion of the liquid displaced during the return stroke of said control member, thereby to decelerate said return stroke, whereby said control member upon the attaining of a predetermined r.p.m. and at a certain value of the crosssectional area of said restriction is subjected to a fluid abutment and does not return to said initial position, a second bypass connected with said work chamber and means on said control member for controlling said second bypass, a slide valve driven in synchronism with said injection pump and said auxiliary pump for controlling said second bypass, characterized by a dimensioning of said system, whereby said second bypass (33) is opened up by said control member (14) before said first bypass (16), said second bypass (33) in the absence of a fluid abutment being closed by said slide valve (2) before being opened by said control member (14) and in the presence of said fluid abutment being opened by said control member (14) for increasing levels of said fluid abutment at an increasingly earlier time relative to the earlier closing thereof by said slide valve (2), a throttling restriction (35) being provided in said second bypass (33).
 2. A fuel injection system according to claim 1, in which the cross-sectional area of said throttling restriction (35) is variable.
 3. A fuel injection system according to claim 1, in which said slide valve (2) comprises the piston of said injection pump.
 4. A fuel injection system according to claim 1, in which said slide valve (2) comprises the piston (18) of said auxiliary pump.
 5. A fuel injection system according to claim 1, in which there are provided on said control member (14) for controlling said bypasses (16, 33) an annular notch (17), a longitudinal notch (37) connecting therewith and an end surface delimiting said longitudinal notch (37) in the axial direction for controlling said second bypass (33), said longitudinal notch (37) having a throttling restriction (35a). 